Impact of waves and storms on salt marsh erosion and sedimentation dynamics
Date
2024
DOI
Authors
Version
OA Version
Citation
Abstract
Salt marshes are dynamic coastal environments that continuously undergo lateral and vertical changes due to erosion and sedimentation dynamics that are mediated by physical and biological processes. This dissertation focuses on edge erosion and the drivers behind this form of marsh loss, as well as sedimentation of the marsh platform from storms and the potential sources of these sediment influxes. By studying these erosion and sedimentation dynamics in a variety of marshes, this dissertation contributes to our understanding of sediment movement in marsh systems and the drivers of marsh loss and resilience. The marsh edge is vulnerable to wave attack, which can dislodge sediment or induce mass failure through undercutting and destabilizing action of the edge. Vegetation and geotechnical properties affect the erodibility of the marsh edge, and all these factors interact to enhance or mitigate edge erosion and produce certain marsh edge morphologies. The first chapter of this dissertation investigates these different parameters and their relationship to the type and distribution of edge erosion occurring in the Great Marsh, Massachusetts. This work demonstrates that there is no clear relationship among wind fetch, geotechnical properties, and the type of edge erosion observed because of heterogeneity of the marsh. Marsh edges can erode in both exposed and sheltered areas, and the geotechnical characteristics of the marsh edge do not serve as indicators of edge erosion. Parameters and processes beyond those generally ascribed to be the drivers of edge erosion may therefore be responsible for marsh loss. The second chapter takes a closer look at the relationship between waves and marsh shoreline retreat, as the nature of this relationship can help predict marsh loss under varying wind and wave conditions, as well as have implications on the impact of storms on edge erosion and marsh loss. This study shows that there is no universal or generalizable linear relationship between wave power and retreat as previously suggested, but rather the relationships between these parameters are site-specific and are often not linear at all. As a result, in one marsh, storms may have an outsized impact on retreat, while in another marsh more moderate wind-wave conditions may contribute to most of the retreat. Thus, it is important to calibrate these relationships for each marsh to fully constrain marsh loss due to wave attack and predict future marsh erosion. This work further highlights the importance of utilizing statistically robust analyses and regressions to investigate these relationships.
Whereas storms contribute to marsh loss via edge erosion, they can also enhance vertical accretion and resilience of marshes to sea level rise (SLR) through storm-driven sediment transport and deposition. Major storms such as hurricanes can provide most of the inorganic sediment delivered to the marsh platform, though the source of these sediments is less understood for southeastern USA. Chapter 3 of this dissertation characterizes foraminifera communities in Hurricane Irma deposits in Sapelo Island, Georgia and compares them with the communities of surrounding sediment reservoirs to investigate the provenance of these storm-derived deposits. The foraminifera in the hurricane deposits resembled the foraminifera found in the surrounding marsh, rather than nearby sediment reservoirs such as tidal flats, channels, and offshore sediments. These similarities between the storm and marsh foraminifera assemblages are attributed to a mix of two processes: resilience of marsh foraminifera and rapid recolonization of these communities in the storm deposits following the passage of Hurricane Irma, and some reworking of marsh sediments into the storm deposits during the hurricane’s storm surge. The study also assesses the utility of foraminifera in identifying storm deposits, which has implications for the sensitivity of foraminifera paleostorm studies.
Description
2024
License
Attribution-NonCommercial-NoDerivatives 4.0 International